I have gone and played the game you linked, it is exactly as I remember it! great find, Thank you.

OK on to business here. What I understand of your description seems different then how the game works. heres what I think you are trying to do. You only want to allow the player to shoot the first (or last) number in the line? This will make it VERY hard to play. But maybe thats not what you mean.

Heres what I assumed you wanted to do, If here are 3 sevens in the display, every time i hit fire with my aim number being 7, it will remove the left most occurance of the 7. Then any numbers further to the left will move right. In that way, if the player has 3 sevens, and can press fire 3 times before a new number is added, the targets are now fewer. The orginal game had a preset number of targets to shoot for each level. When all were shot without letting them reach the : level was complete. next level, numbers appear faster.

so here is what I am trying to suggest:
assume we have only 5 elements in the array (make bigger to suit your game but the theory will be the same)

t(0) t(1) t(2) t(3) t(4) t(5) #t(5) is the : if t(5) <>" ", you lose

upon starting the game t(all) = " "
when a new number is added, it comes in at t(0). to do this, first shift everybody right, maybe like this:
t(5)=t(4)
t(4)=t(3)
t(3)=t(2)
t(2)=t(1)
t(1)=t(0)
t(0)=new target
if t(5)<>" " you lose

update LCD

now for the fire check:
scroll through the array checking for equal:

index=4
start check
if t(index)<>bullet
index=index-1
if index<0 then no hit
goto start check
else hit
now lets say t(2) = bullet

for shift = index to 4
t(shift)=t(shift+1)
next shift

now update LCD with new array!
wait in mainloop until either aim is pressed, fire is pressed or scroll timer says add a number

I purposely did not put use code tags because I am not sure this would be compilable code. I am new to PBP and don't have all the syntax in my head yet. I am really just trying to show you ONE way of approaching this. Of course a loop would be much better for the shift, and I'm sure I have left plenty of stuff out, but maybe this will help.